Although the average accuracy of autorefractors is very good, they still cannot be reliably used to write eyeglass prescriptions because about 20 percent of patients will be measured differently by subjective refraction by at least 0.5 diopters. Further, the patients that are measured differently have the same error on autorefractors made by many different manufacturers. This indicates that there is some structural difference in those eyes. We hypothesize that the significant structural difference is that the spacing between the photoreceptors to the choroid blood supply is different in those patients relative to the general population. We propose a method to measure the photoreceptor to choroid spacing and a method to use that parameter to improve the calculated spherical equivalent power on those patients. Means are also provided to test the hypothesis that the Stiles Crawford effect is responsible for the difference in autorefractions versus subjective refractions. Expected benefits of this research include improved and earlier detection of various retinal pathologies, potential benefits for diabetic patients and others. Medical practice is anticipated to benefit through advancements in automated refraction techniques.